Pay telephones, hotel house telephones, and the like are usually installed in some form of enclosure. Sometimes the enclosure is a four-sided booth. In other cases, it is simply a partial shelter under which a person can stand while using the telephone. It is desirable that the enclosure of whatever kind shall provide some kind of illumination to assist the user in locating and dialling telephone numbers, inserting coins, writing notes, and the like. In the past, the illumination has usually been provided in an essentially utilitarian manner at minimal cost. The enclosure, and its illumination, however simple it might be, represented an installation expense, which was paid for only out of the user fees paid for the use of the telephone.
It is however a fact that the person using the telephone is a captive audience, for any information which it may be possible to display around the telephone. This makes it a particularly suitable location for erecting advertising, which can earn revenue in addition to the user fees.